Hepatitis B virus is a major cause of liver cirrhosis and hepatocellular carcinoma (HCC). A better understanding of the viral life cycle may provide targets for the intervention of HBV infection, thus reducing the risk of HBV-related HCC. However, the early stages of the viral life cycle and viral-host interactions that contribute to viral infection and pathogenicity are poorly understood. This 421 exploratory proposal focuses on studies on a hepadna virus interacting protein, p120/glycine decarboxylase. We have previous found that p120 is a binding partner of an avian hepatitis B virus envelope protein. It is expressed only in the virus infectable tissues and its expression level is directly correlated with the cellular susceptibility to virus infection. It is expressed only in the virus infectable tissues and its expression level is directly correlated with the cellular susceptibility to virus infection. Moreover, viral mutants with an ablated p120-binding site showed reduced infectivity despite wild-type replication capacity. These findings suggest that p120 is associated with the early stage of the viral life cycle. Therefore, we plan to further establish its role in the viral life cycle by genetic approaches. Specific Aim #1 will determine if inhibition of p120 expression or function in well-differentiated duck hepatocytes will reduce susceptibility to viral infection. Specific Aim #2 will examine whether reconstitution of p120 in de-differentiated duck hepatocytes will restore productive viral infection. In addition, we will determine if p120 is defective in Muscovy ducks, a duck species resistant to hepadnavirus. We will also explore the possibility to restore viral infection by p120 derived from a susceptible Pekin ducks. These studies will provide further information on virus-cell interactions and may lead to development of novel anti-viral strategies for prevention of HBV induced liver cancer.